1. Field of the Invention
The present invention relates to a lateral force estimation system, a method of estimating a lateral force, and a vehicle including the lateral force estimation system.
2. Description of the Related Art
A lateral force of a wheel is required to be accurately estimated to control travelling of a vehicle. Regarding a four-wheeled automobile, a posture of a vehicle body during travelling is substantially constant, so that the lateral force is relatively easily and accurately estimated. On the one hand, regarding a vehicle that turns with a vehicle body being tilted with respect to a ground surface (a motorcycle, for example), forces in various directions are exerted on a wheel, so that it is difficult to accurately estimate the lateral force.
In JP 2006-240491 A, a method for calculating a lateral force actually exerted on a tire based on a lateral force of a tire generated by a roll angle (a camber thrust) is disclosed. Specifically, a relationship among a lateral slide angle of the tire, the roll angle (a camber angle), and the lateral force is measured in advance, and a camber thrust map is produced based on the results of the measurement. The camber thrust map shows a relationship among the roll angle, the lateral slide angle, and the camber thrust. The camber thrust is calculated using this camber thrust map. The lateral force actually exerted on the tire is calculated based on the calculated camber thrust.
However, the lateral slide angles of the tires are different from one another depending on the properties of the tires such as an air pressure and rubber properties. Therefore, when the tire properties change, accuracy of the calculated lateral force decreases. Further, when the roll angle is stably maintained during the travelling of the vehicle, a lateral force having a relatively high accuracy is acquired using the above-mentioned map. On the one hand, when a posture of a rider changes or the roll angle changes during the travelling of the vehicle, a lateral force having a high accuracy is not acquired even when the above-mentioned map is used.